Trip lock device for a snow plow

ABSTRACT

A trip lock device for replacing a return spring of a snow plow assembly having a trip mechanism. The device includes an extensible body having a first end for connection to a moldboard a second end for connection to a plow frame. A limiting member is provided to the extensible body to limit its range of extension. A method of installing the device involves removing a return spring from a first and second mounting locations and attaching the extensible body to the first and second mounting locations. The device may also include a load-limiting frangible link.

BACKGROUND OF THE INVENTION

The present invention relates to snow plow assemblies and more particularly to, to vehicle mounted snow plow assemblies that employ obstacle responsive trip mechanisms.

Trip mechanisms are provided on many snow plows in order to allow the moldboard (plow blade) to pivot downward when the bottom edge of the moldboard contacts an obstacle that it is unable to move. As a result, the moldboard lifts upward, allowing it to move over the top of many low lying obstacles, such as rocks, curbs, etc., thereby reducing the possibility of damage to the plow and/or the obstacle. A return mechanism, typically consisting of several helical extension springs attached between the moldboard and the plow frame, causes the moldboard to return to its normal operating position once the obstacle is cleared.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a trip lock device comprising a piston, a rod and a cylinder assembly that limits the range of travel of the moldboard of a snow plow assembly having a trip mechanism. According to a further aspect of the invention, the trip lock device includes a load limiting frangible link.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a snow plow assembly having a trip lock device according to the present invention attached thereto;

FIG. 2 is a side view of the snow plow assembly of FIG. 1;

FIG. 3 is a top view of a portion of the plow assembly of FIG. 1;

FIG. 4 is a perspective view of a portion of the plow assembly of FIG. 1, illustrating details of the trip lock mechanism attached thereto; and

FIG. 5 is a sectional view of the trip lock device of FIG. 1, shown partially schematically.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1-4, a snow plow assembly 10 is shown attached to the front of a vehicle. The plow assembly 10 includes a trip mechanism, wherein a moldboard 12 is connected a plow frame 14 in such a way that the moldboard 12 can pivot away from the plow frame 14 in a known manner. The trip mechanism also includes several helical return springs 16 attached between the moldboard 12 and the plow frame 14 to bias the moldboard 12 toward an upright position. As shown in FIGS. 1-4, the moldboard 12 is being maintained in a tripped position by a street curb 18.

According to an embodiment of the present invention, a trip lock device 20 is also attached between the moldboard 12 and the plow frame 14. As best seen from FIGS. 3 and 4, the trip lock device 20 includes a cylinder 22 having an internal piston 23 connected to a connecting rod 24 (see FIG. 5). The piston 23 and the rod 24 can move into and out of a first end 26 of the cylinder 22 over a set range. A second end 28 of the cylinder 22 is attached to the plow frame 14. A free end 30 of the piston rod 24 is attached to the moldboard 12. The first end of the cylinder has a lip or end stop 31 to define the maximum limit of the set range. The lip 31 prevents the piston 23 from moving past the first end 26 of the cylinder 22. The minimum limit of the set range is dictated by the length of the cylinder 22 and the length of the rod 24. If the rod 24 is longer than the cylinder 22, then the maximum limit of the set range is the point at which the piston 23 is stopped by an inside surface 32 at the second end 28 of the cylinder 22. Otherwise, if the rod 24 is shorter than the cylinder 22, then the minimum limit of the set range is the point at which the rod 24 is fully inserted within the cylinder up to the point of attachment of the rod 24 to the moldboard 12.

Alternatively, the set range can be made adjustable by providing a means for shortening and lengthening the connecting rod 24, for example a threaded attachment of the rod 24 to the moldboard 12 or the piston 23. As a further alternative, the attachment of the trip lock device 20 can be reversed, such that the second end 28 of the cylinder 22 is attached to the moldboard 12 and the free end 30 of the piston rod 24 is attached to the plow frame 14.

In order to install the trip lock 20 on an existing snow plow 10, one of the plow's return springs 16 can be removed and the trip lock 20 attached in its place using the existing mounting means 32,34. This eliminates the need for extensive retrofitting of the snow plow 10. In the disclosed embodiment, the mounting means 32 provided to the moldboard comprises an eye bolt and the mounting means 34 provided to the plow frame 14 comprises a flange having a hole. Alternatively, any suitable mounting means may be used.

It should be appreciated that, alternatively, by providing an additional mounting means on the snow plow assembly, a trip lock device 20 according to the present invention can be simply and easily integrated into an OEM (original equipment manufacturer) snow blade assembly or installed on an existing snow plow assembly without removing any return springs.

With the trip lock device 20 of the present invention installed on the snow plow assembly 10, the range of travel of the moldboard 12 during tripping is limited to the range of the piston 23 within the cylinder 22. This will prevent the extension springs 16 from being overextended while the moldboard 12 is tripped. The range of travel can be adjusted as appropriate by moving the piston 23 closer to or further from the free end of the rod 24, for example by adjusting a threaded connection (not shown) between the rod 24 and the piston 23.

Additionally, a sheer pin or bolt 36 is provided in the connection between the second end 28 of the cylinder 22 and the plow frame 14 to act as a load-limiting frangible link. As a result, if the snow plow 10 continues to move toward an obstacle, such as the curb 18, after the limit of travel is reached, the bolt 36 will sheer after a set load limit is reached, thereby disconnecting the trip lock 20 from the plow frame 14.

It should be evident that this disclosure is by way of example and that various changes maybe made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure. 

1. A trip lock device for replacing a return spring of a snow plow assembly having a trip mechanism, the device comprising: an extensible body comprising a first end for connection to a moldboard of a snow plow assembly, and a second end for connection to a plow frame of the snow plow assembly; and a limiting member provided to the extensible body to limit a range of extension of the extensible body.
 2. The trip lock device of claim 1, wherein the extensible body comprises a cylinder and a connecting rod.
 3. The trip lock device of claim 2, wherein the first end of the extensible body comprises a free end of the connecting rod and the second end of the extensible body comprises an end of the cylinder.
 4. The trip lock device of claim 1, wherein the limiting member comprises a piston.
 5. The trip lock device of claim 1, further comprising a load-limiting frangible link for connection between a snow plow assembly and one of the first end of the extensible body and the second end of the extensible body.
 6. The trip lock device of claim 5, wherein the load-limiting frangible link is one of a sheer pin and a sheer bolt.
 7. The trip lock device of claim 1, wherein the extensible body further comprises an adjustment mechanism for adjusting the range of extension.
 8. The trip lock device of claim 7, wherein the adjustment mechanism comprises a threaded connecting rod.
 9. A method of installing a trip lock device on a snow plow assembly comprising the steps of: removing a first end of a return spring from a first mounting means provided on a moldboard of the snow plow assembly; removing a second end of a return spring from a second mounting means provided on a plow frame of the snow plow assembly; attaching a first end of an extensible body of the trip lock device to the first mounting means; and attaching a second end of the extensible body to the second mounting means.
 10. The method of claim 9, wherein the extensible body comprises a cylinder and a connecting rod.
 11. The method of claim 10, wherein the first end of the extensible body comprises a free end of the connecting rod and the second end of the extensible body comprises an end of the cylinder.
 12. The method of claim 9, wherein the trip lock device further comprises a limiting member provided to the extensible body to limit a range of extension of the extensible body.
 13. The method of claim 12, wherein the limiting member comprises a piston.
 14. The trip lock device of claim 9, further comprising a load-limiting frangible link for connection between a snow plow assembly and one of the first end of the extensible body and the second end of the extensible body.
 15. A trip lock device for replacing a return spring of a snow plow assembly having a trip mechanism, the device comprising: a connecting rod comprising a first end and a second end, a cylinder having a longitudinal axis, a first end for connection to a plow frame of the snow plow assembly and a second end for receiving the first end of the connecting rod, a piston attached to the first end of the connecting rod, the piston being movable along the longitudinal axis within the cylinder to limit a range of extension of the extensible body; and a load-limiting frangible link for connection between a snow plow assembly and the end of the cylinder. 